WO 2007/118500 A1 describes a device for storing hydraulic fluid of a hydraulic system of a transmission device, which has at least one storage chamber that is delimited by a housing assembly and a delimiting device and which can be brought into functional connection with a hydraulic system for exchanging hydraulic fluid, the volume of the storage chamber being variable between a minimum and a maximum depending on the operating condition of the delimiting device and/or that of the housing assembly. The delimiting device and/or the housing are held by a holding device at least in the operating condition that is equivalent to the maximum volume of the storage chamber, in opposition to a restoring effort of the housing assembly and/or the delimiting device which, starting from an operating condition which differs from the operating condition that is equivalent to the minimum volume of the storage chamber, is directed toward its operating condition equivalent to the minimum volume of the storage chamber.
The device, which comprises a pulse store, is combined with a transmission device in order to bring, during a motor start, the transmission device within desired operating times to an operating condition in which the shifting elements to be engaged, in order to produce a required operating condition of the transmission device, such as clutches and/or brakes as well as a hydraulic control unit, are supplied with hydraulic fluid to an extent necessary for this. During this a transmission pump that can be driven by the motor, in combination with the device, is capable of producing in the area of the clutches and/or brakes a desired operating condition or a frictional engagement. Without the hydraulic fluid volume stored in the area of the device, the shifting elements and the hydraulic control unit of the transmission device are only after the lapse of longer operating times filled to the desired extent or supplied with the necessary hydraulic fluid volume.
To be able to further reduce the consumption of energy of the drive machines of vehicles, for example the power uptake of such a transmission pump of a transmission device can be reduced by making the transmission pump smaller. However, a smaller transmission pump is in some circumstances problematic, if shifts, at low rotational speeds of the drive machine, can only be assisted insufficiently by the smaller transmission pump, since such transmission pumps cannot then deliver enough hydraulic fluid to make up for transmission leaks and fill the shifting elements to be actuated. Examples of critical shifts are engaging a gear while the vehicle is stationery, or so-termed roll-off shifts.
In order to make available a sufficient hydraulic fluid volume, even during the above-described supply-critical operating condition situations, for example a further, spring-loaded hydraulic fluid volume store can be used by means of which, if critical operating conditions occur, a stored hydraulic fluid volume can be delivered to the hydraulic system in addition to the hydraulic fluid volume provided by the transmission pump. However, such a further hydraulic store takes up additional space and considerably increases the manufacturing costs of a transmission device.
The device known from WO 2007/118500 A1, also comprising a spring-force-actuated hydraulic store that can be triggered by an electrical detent system, delivers a hydraulic volume pulse during a drive machine starting process to the hydraulic system of a transmission device and thereby assists with the filling of the shifting elements being shifted for the required frictional connections. In principle the known device and its store can also be used during the normal operation of a vehicle's drive-train to assist shifts, during which the electrical detent or holding device is deactivated. However, with such actuation of the device, during a start of a drive machine there is no guarantee that the device will provide a desired hydraulic fluid volume, since it is necessary to have a correspondingly full store to meet that requirement in any and all operating conditions of a transmission device or vehicle drive-train. This means that by way of the device known from the prior art, either only a start can be assisted, or for example, shift assistance is possible during normal operation.